(1) Field of the Invention
The present invention is related to a rotary power transmission mechanism for transmitting rotary power to a cylindrical member. In particular, the present invention relates to a rotary power transmission mechanism that transmits rotary power from a shaft that passes through a central area of a flange member to the flange member, which is fitted to an end portion of the cylindrical member, thus rotationally driving the cylindrical member, and to a photoreceptor drum device, developing device, fixing device, and image forming device provided with the rotary power transmission mechanism.
(2) Description of the Related Art
For example, an image terming device that forms images by the electrophotographic method, such as a photocopying machine or a printer, includes a photoreceptor drum that is a cylindrical member that is rotationally driven.
Such an image forming device usually has a structure in which the photoreceptor drum is a center around which are disposed a charging device, an exposure device, a developing device, a transfer device, and a cleaning device, in this order.
In such a structure of an image forming device, a surface of the photoreceptor drum, which is rotated, is uniformly charged by the charging device. The charged area of the photoreceptor drum is exposed to optically modulated laser light from the exposure device. A latent electrostatic image formed on the surface of the photoreceptor drum by the exposure is developed by the developing device.
The developing device has a developing roller disposed parallel to the photoreceptor drum and a predetermined gap (hereafter, “developing gap”) exists between the developing device and the photoreceptor drum. The latent electrostatic image is visualized on the surface of the photoreceptor drum as a toner image by toner that is carried by a surface of the rotating developing roller and conveyed to a position facing the photoreceptor drum.
Meanwhile, a recording sheet is supplied from a paper feed device and is conveyed to a position at which the photoreceptor drum and the transfer device face each other. The toner image on the photoreceptor drum, receives the effect of an electric field generated by the transfer device, and transferred onto the recording sheet. Alternatively, in an image forming device using an intermediate transfer system, the toner image on the photoreceptor drum is temporarily transferred to an intermediate transfer body, such as an intermediate transfer belt, then transferred to the recording sheet.
Toner not transferred to the recording sheet or the intermediate transfer body and that is left on the surface of the photoreceptor drum, byproducts of electrical discharge generated by the charging process, and other such attached matter is scraped off by the cleaning device, whereby the surface of the photoreceptor drum is cleaned.
As the cleaning device, a blade cleaning system is widely used, in which one edge of a cleaning blade composed of polyurethane rubber, etc., is pressed against the surface of the photoreceptor drum, removing the attached matter by mechanical force.
The photoreceptor drum described above is rotationally driven by motive power transmitted from a rotational power source such as a motor through a motive power transmission mechanism (for example, refer to Japanese Patent Application Publication No. 2002-182527, Japanese Patent Application Publication No. 2007-24085).
A structure of a final stage of a conventional motive power transmission mechanism is explained below with reference to FIGS. 8A, 8B, 8C, 8D and 8E.
FIG. 8A is an exploded perspective view schematically showing a photoreceptor drum 200 and a final stage portion of the motive power transmission mechanism mentioned above. FIGS. 8B and 8C show the final stage portion in an assembled state, viewed in a direction along an arrow Q in FIG. 8A. FIGS. 8D and 8E are illustrations that additionally include a cleaning blade 202 and a developing roller 204 for explaining a problem with conventional technology.
As shown in FIG. 8A, a first flange member 206 made of synthetic resin is provided at one end of the photoreceptor drum 200, and a second flange member 208 made of synthetic resin is provided at another end of the photoreceptor drum 200. The first flange member 206 has a through hole 206A through the center thereof, and the second flange member 208 has a through hole 208A through the center thereof. A shaft 210 is inserted to pass through both of the through holes 206A and 208A.
In an end surface of the first flange member 206 opposite an end surface facing a center of the photoreceptor drum 200, a first slit 2061 and a second slit 2062 are formed extending outward from the through hole 206A in opposite radial directions of the first flange member 206. The first slit 2061 and the second slit 2062 have a width less than the diameter of the through hole 206A.
In the shaft 210, an insertion hole 210A is provided that passes through the shaft 210 in a radial direction of the shaft 210. The insertion hole 210A is for inserting a parallel pin 212.
According to the configuration described above, the first flange member 206 is fitted to the one end of the photoreceptor drum 200 and the second flange member 208 is fitted to the other end of the photoreceptor drum 200. The parallel pin 212 is then inserted into the insertion hole 210A of the shaft 210.
The shaft 210, into which the parallel pin 212 has been inserted, is inserted into the through hole 206A of the first flange member 206. The shaft 210 passes through the photoreceptor drum 200, and then passes through the through hole 208A of the second flange member 208.
Finally, both side portions of the parallel pin 212 that are protruding from the shaft 210 are inserted into the first slit 2061 and the second slit 2062, completing the assembly.
As shown in FIG. 8B, when an axial center of the parallel pin 212 coincides with a center of the first slit 2061 and the second slit 2062, a size of a gap d1 between the parallel pin 212 and side walls of each of the first slit 2061 and the second slit 2062 is 0.1 mm-0.2 mm. Also shown in FIG. 8B, when both ends of the parallel pin 212 protrude equally from the shaft 210, a size of a gap d2 between an end surface of the parallel pin 212 and a corresponding one of an end wall of the first slit 2061 and the second slit 2062 is 0.3 mm-0.5 mm.
According to the above configuration, when the shaft 210 is rotated in the direction indicated by an arrow P, as shown in FIG. 8C, both ends of the parallel pin 212 contact with and push against a corresponding one of a side wall of the first slit 2061 and a side wall of the second slit 2062 (a force Fa and a force Fb). The force Fa and the force Fb act together as a coupled force to rotate the first flange member 206 about an axial center of the shaft 210. Thus, the photoreceptor drum 200, which is fitted to the first flange member 206, is rotationally driven.
However, according to the conventional configuration described above, considering the ease of assembly of the parallel pin 212 and the shaft 210, and the ease of disassembly of the parallel pin 212 and the shaft 210, the parallel pin 212 is slidably inserted into the through hole 210A (a so-called “clearance fit”), and therefore the parallel pin 212 moves in an axial direction thereof during rotation. As a result, as shown in FIGS. 8D and 8E, only one end of the two ends of the parallel pin 212 contacts a corresponding one of the side wall of the first slit 2061 or the side wall of the second slit 2062, and pushes the first flange member 206 (hereafter, “single push state”).
During rotation, variation in the width of the developing gap as a result of the above has been identified. This variation is thought to occur for the following reason.
At a circumferential surface of the photoreceptor drum 200, as shown in FIGS. 8D and 8E, the cleaning blade 202 presses against a location in a circumferential direction of the photoreceptor drum 200, as described above. Thus, a force Fc acts on the first flange member 206 in a tangential direction thereof, and resists rotation of the first flange member 206, and a force Fd acts on the first flange member 206 in a radial direction thereof. In such a case, the force Fd, which acts in the radial direction of the first flange member 206, deforms the first flange member 206, causing the first flange member 200 to be closer to the developing roller 204.
When in the single push state and while the first flange member 206 is undergoing one rotation, an angular position of pushing force from the parallel pin 212 on the first flange member 206 changes relative to a point at which the cleaning blade 202 presses against the photoreceptor drum 200. For example, as shown in FIG. 8D, when a pushing force FA acts in the same direction as the force Fd, the pushing force FA works with the force Fd, causing the first flange member 206 to be closer to the developing roller 204 than when the force Fd acts alone. As shown in FIG. 8E, when the pushing force FA acts in an opposite direction to the force Fd, the pushing force FA resists the force Fd, causing the first flange member 206 to be farther from the developing roller 204 than when the force Fd acts alone.
Thus, it can be considered that shifting of the photoreceptor drum 200 has a cycle corresponding to one rotation of the first flange member 206 (one rotation of the photoreceptor drum 200), causing variation in the width of the developing gap. Due to variation in the width of the developing gap, a problem occurs of darker or lighter than intended areas arising in an image formed by the image forming device.
To address this problem it may seem sufficient to adopt a configuration in which the parallel pin 212 is press-fitted to the insertion hole 210A such that the parallel pin 212 does not move in the axial direction thereof. However, this is not a realistic option since press-fitting the parallel pin 212 while adjusting the both ends of the parallel pin 212 to protrude by an equal length from the shaft 210 would be very labor-intensive and ease of assembly would be considerably reduced.
Note that the problem described above is not limited to cases in which rotary power is transmitted from a shaft to a photoreceptor drum. The problem is common to other cylindrical parts, for example, when transmitting rotary power to a developing roller that includes a developing sleeve. Furthermore, the problem is common to rotary power transmission mechanisms in general, which transmit rotary power from a shaft to a cylindrical member through a pin member and a flange member.